1. Field of the Invention
The present invention relates to the recrystallizing of polycrystalline or amorphous or small grain material to produce as large a grain size as possible, and more particularly is directed to growing a single crystal structure by recrystallizing a polycrystalline or amorphous upper layer extending over an electrically isolating layer on a single crystal semiconductor substrate.
2. Description of the Prior Art
In growing a single crystal film from a polycrystalline or amorphous layer extending over an electrically isolating substrate, it has been proposed to use various conventional energy sources, such as, a spot laser beam, spot electron beam, graphite strip heater or arc strip lamp, to scan and thereby melt the polycrystalline layer so as to induce liquid or solid phase regrowth by epitaxial recrystallization.
However, such conventional energy sources have proven to be unsatisfactory. When spot beam energy sources are used to melt the polycrystalline layer, the resulting recrystallized layer typically lacks a uniform single crystalline structure. Such nonuniformity is due to the circular cross section of the beam which requires that the spot beam repeatedly scan the polycrystalline layer along overlapping paths, so that portions of the polycrystalline layer constituting 70 to 80 percent thereof are scanned more than once. Spot beam energy sources in repeatedly scanning portions of the polycrystalline layer, require an undesirable amount of time in order to scan the entire surface of the polycrystalline layer. Furthermore, the single crystalline structure that is obtained is not of high quality.
In employing conventional strip beam energy sources, such as, graphite strip heaters or arc strip lamps, to melt the polycrystalline layer, damage can occur to the underlying electrically isolating layer and semiconductor substrate. More particularly, such conventional strip beam energy sources cannot be sufficiently focused so that the energy density of the strip beam at its area of impact with the polycrystalline layer is less than desirable. Consequently, a relatively long time of contact of the beam with the polycrystalline layer is required to melt the latter which results in dissipation of an unacceptable amount of heat from the polycrystalline layer and possible damage to the underlying isolating layer and substrate. For example, a strip beam from a conventional strip arc lamp has to contact a polycrystalline layer of a thickness of one to three microns for about one second in order to melt such layer.